textproduct: Quad Cities

KEY MESSAGES

- Chances for showers/storms return this evening and overnight as a weak cold front arrives in the area.

- High pressure will bring a period of much needed quiet and dry weather Sunday through Monday, prior to the pattern becoming more active Tuesday through midweek.

SHORT TERM /THROUGH TONIGHT/

Issued at 214 AM CDT Sat Aug 15 2026

Modest LLJ and stationary boundary near our south has allowed for widespread storms to develop south of Interstate 80. These areas have seen rounds of storms, which are producing heavy rainfall and frequent lightning. There remains a Marginal Risk, level 1/5, for severe weather tonight, with main concerns being precipitation loaded downdrafts producing severe gusts. At this time, confidence is low, with the threat being relatively isolated. Our main concern will be heavy rainfall and flash flooding for the remainder of the night. Locations south of Interstate 80 have already seen rounds of heavy rainfall, with this continuing into early Saturday morning. PWATs over 2.00" are being seen area- wide, with our 00z DVN Balloon coming in with 2.09". Thus, areas of repeating showers/storms can easily see upwards to 2.00"+ of rain, with higher amounts likely. HREF guidance comes in quite high on rainfall, bringing in a swath of very heavy rainfall between the Interstate 80 and Highway 34 corridors. Observational trends have indicated the heaviest swath of rain is currently along/south of Highway 34 so far tonight, which is where we might actually see these higher totals. Although, a strengthening LLJ will push farther north through the night, which may nudge this current axis north a bit. The HREF PMM continues to show the potential for at least 3.00-5.00"+ in the hardest hit areas. Locally higher amounts will be possible. As such, the WPC continues to highlight our area in a Moderate Risk, level 3/4, for Excessive Rainfall and Flash Flooding into Saturday morning. The Flood Watch will remain in effect into mid-morning Saturday.

Saturday morning, we will start to see the thunderstorm activity decrease from west-east, with much of the area trending dry by midday. By late afternoon, a remnant boundary from overnight convection will be draped over the area, roughly near the Interstate 80 corridor. The LLJ will start to increase as another wave moves into western Iowa and tracks east through the day. We will start to see isolated to scattered showers/storms develop along this axis, with coverage increasing into the evening/overnight hours. This wave will push through the area overnight Saturday, dragging a cold front through as well. With this pattern in place, we will once again see a round of overnight showers/storms. Overall, shear will be lower, yet sufficient for a few organized thunderstorms, with sufficient instability for some stronger storms with lightning. PWATs will be well above seasonal norms, generally ranging between 2.00-2.25". Thus, heavy rainfall can be expected in any thunderstorms Saturday night into Sunday AM. Although, this system will feature weaker overall forcing and be more progressive, which should help keep areas of heavier rainfall more localized. Heaviest hit areas can see upwards to 1.00-2.00" of rain from this round of storms, with <1.00" elsewhere. A localized flash flood threat will be seen, with WPC highlighting the whole area in a Marginal Risk, level 1/4, for Excessive Rainfall and locations in west-central Illinois in a Slight Risk, or level 2/4 threat.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 214 AM CDT Sat Aug 15 2026

Sunday Through Monday...

This timeframe will be relatively quiet, as we will be fully post frontal and generally in cool/dry advection by midday Sunday. Upper wave and cold front will be east of the area by early Sunday morning, which will effectively help flatten the ridge that was set up over the area the last week, which brought persistent rainfall. Thus, this will shunt the active baroclinic zone south of the area, with surface high pressure passing over through Monday. A period of quiet and dry weather will be seen, with near seasonal temperatures. Monday looks to be a beautiful day with mostly clear skies. Enjoy this reprieve from the active stretch of weather that the region has been experiencing, as the pattern becomes active once again Monday night through midweek.

Tuesday and Beyond...

Monday night into Tuesday, weak ridging will pass east of the area, pushing the surface high pressure out and resulting in increasing llvl southwesterly flow. Temperatures and moisture will both increase on Tuesday, with best moisture moving in later in the day. LLJ will kick in Tuesday evening and through the night, as a quick- moving upper wave approaches the area from the northwest. A seasonally strong cold front will accompany this wave, providing sufficient surface and upper level forcing for thunderstorms. A brief look at model soundings during this timeframe would indicate the potential for an overnight complex of thunderstorms passing through the area, as we have seen over the last week. The main difference with this system is that it will be progressive, pushing out of the area by early-midday Wednesday and leaving us in a post- frontal airmass through the remainder of the week. The best moisture will move into the area ahead of the cold front Tuesday night, with global guidance indicating 1.50-2.00" PWATs moving in. Thus, heavy rainfall will be on the table with these storms. It's too early to dive into the severe threat, but given the pattern and environment in place, a few stronger storms will be possible.

After this wave pushes out of the area on Wednesday, we will see weak zonal-northwesterly flow set up again over the region. Surface high pressure will pass through late in the week, which should bring a period of mostly dry weather. Although, there remains some uncertainty, as some long term models indicate subtle waves passing through bringing low-end PoPs. NBM favors the mostly-dry forecast, leaving PoPs <20% through Friday. The post-frontal airmass will keep temperatures cooler through the second half of the week, with most in the mid 70s.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1216 PM CDT Sat Aug 15 2026

Widespread moisture continues to be found in the lower atmosphere over eastern Iowa and Illinois. This is resulting in widespread IFR/MVFR cloud cover and a few light showers. The visibility will generally be above 6 miles today, except near DBQ where drizzle will continue a bit longer before lifting north. Following many dry, but low cloud filled hours this afternoon, a cold front arriving between 04z and 10Z tonight will bring a threat for storms, with hourly coverage of 30-50%, resulting in a Prob30 group for thunderstorms included at all terminals later tonight for around 3 hours. Once this area of storms rolls east of the area late tonight, more MVFR clouds and possibly some fog will move back in. While winds will shift northwest, the air will remain damp through Sunday.

HYDROLOGY

Issued at 1225 PM CDT Sat Aug 15 2026

Rainfall ranging from 2 to 6 inches, across southern parts of the area, mainly south of the tributary forecasts it was expected to fall 24 hours ago. This is a helpful thing, though flooding did impact portions of McDonough through Lee County overnight, and this warranted minor flood warnings for the Skunk River at August today, and a moderate flood warning for Colmar, on the La Moine River.

Flood warnings and watches on portions of the Iowa, Wapsipinicon, and upstream Skunk have been cancelled, as this rainfall fell south or downstream of these forecast points.

DVN WATCHES/WARNINGS/ADVISORIES

IA...None. IL...None. MO...None.